1. Field of the Invention
The present invention relates to a light emitting device that can be used in an indicator, a lighting apparatus, a display, a backlight for liquid crystal display etc. More particularly, the present invention relates to a light emitting device that is highly reliable by employing a protective device even when a semiconductor light emitting element having high output is mounted thereon.
2. Background Information
For example, a chip type light-emitting element disclosed in Japanese Laid-Open Patent Application No. 11-54804 comprises an insulating substrate, a pair of terminal electrodes provided on both end parts of the surface of the substrate, a semiconductor light emitting element mounted on one of the terminal electrodes, and a protective element for protecting the semiconductor light emitting element from at least the reverse voltage that may be applied thereto. The protective element is mounted on the other one of the terminal electrodes. Each of the semiconductor light emitting element and the protective element is bonded respectively to an end portion side of the corresponding terminal electrode. A pair of wires for connecting the semiconductor light emitting element and the protective element with the opposite terminal electrodes is connected to pad portions formed integrally with the terminal electrodes.
By forming the terminal electrodes in such shape and by specifying the mounting locations of the semiconductor light emitting element and the protective element and the connecting locations of the wires, defective wire bonding can be prevented, and damages due to applied reverse voltage and high voltage caused by electrostatic charge can be prevented. Thus, a chip type light emitting element with improved reliability can be obtained.
However, when such a pad portion is provided at an end portion of a lead electrode constituting the terminal electrode, a distance between the mounting location of the semiconductor light emitting element or the protective element and the pad portion becomes too large. In other words, in the case in which a metal plate is subject to punching process by way of press working etc., a width approximately the same as the thickness of the plate is needed to form a through hole. Therefore, the distance between the mounting portion and the pad portion becomes larger as the thickness of the plate increases. In such cases, the package is required to be made larger to secure the mounting portions of the elements.
The smaller the thickness of the metal plate, the smaller the distance can be. However, in such cases, not only the strength of the metal plate, but also the strength of the package decreases. Further, the heat dissipation also decreases so that high output power cannot be achieved.
In addition, accuracy of processing a metal plate in a complicated shape, especially such a shape of the pad having a narrow width described in Japanese Laid-Open Patent Application No. 11-54804, is low, and processing of constant shape is difficult to obtain.
Moreover, when the distance between the end portion of the terminal and the lead portion is narrow, resin is difficult to be provided at the time of injection molding, which likely results in defective molding.